This invention relates to a Josephson junction element and to a process for the production thereof.
U.S. Pat. No. 5,534,715 discloses a method of manufacturing YBCO Josephson junctions using a focused Ga ion-beam to damage a substrate before deposition of a YBCO film. The ion-beam irradiation causes implantation of Ga ions into the substrate so that an altered region is formed in the YBCO film at a position just above the irradiated region. As a result, there is formed a SNS structure. This method has a problem in reproducibility. Namely, the superconducting characteristics such as critical current density of the Josephson junction elements vary with elements to elements.
A method is also known which comprises the steps of: irradiating a predetermined portion of a surface of a substrate of a MgO single crystal with a Ga focused ion beam to form a steep slope trench with symmetrical walls in the substrate, depositing YBaCuO superconductor on the surface of the substrate so that a weak link is formed in the YBaCuO layer, and patterning the YBaCuO superconductor layer to form a wiring pattern such that the weak link intersects the wiring pattern. In this method, a superconductor/normal metal/superconductor (SNS) structure is considered to be formed because the crystal orientation of the superconductor in the trench differs from that of the superconductor outside of the trench or because a grain boundary is formed on the trench. With this method, however, the reproducibility of the Josephson junction characteristics is not good.